Against the background of the recent problem of ozone layer depletion, CFC (chlorofluorocarbon) and HCFC (hydrochloro-fluorocarbon) conventionally used as refrigerants for refrigerating machines are subject to regulation and, instead of them, HFC (hydrofluorocarbon) is becoming widely used as a refrigerant. However, one of the HFC refrigerants, HFC-134a, which is commonly used as a refrigerant for car air conditioners, is subject to regulation in Europe due to its high global warming potential (GWP) although its ozone-depleting potential (ODP) is zero.
Under such circumstances, there have been an urgent need to develop a refrigerant that has a small influence on the ozone layer and has a low GWP. For example, Patent Literature 1 discloses a trifluoroethylene (HFO-1123) refrigerant as a refrigerant that has a small influence on the ozone layer and has a low GWP.
In the conventional case where CFC or HCFC is used as a refrigerant, a refrigerating machine oil containing a mineral oil or a hydrocarbon oil such as alkylbenzene has been suitably used. Depending on the type of the coexisting refrigerant, a refrigerating machine oil may show unexpected behaviors in terms of its compatibility with the refrigerant, its lubricating properties, the viscosity of its solution in the refrigerant, or its thermal and chemical stability, which is why different refrigerating machine oils need to be developed for different refrigerants.